Assessment of the water quality and spatial distribution of the major pollutants in Ngerengere River Catchment, Tanzania.

Abstract

Pollution from natural and anthropogenic processes threatens available fresh water resources. This is the case for Ngerengere River in Wami/Ruvu basin in Tanzania. The pollution is aggravated by agricultural and industrial wastewater from upstream sources. The deteriorating water quality poses risks to health and livelihoods, with most affected communities located downstream of the catchment. Few studies have been done on pollution in Ngerengere River catchment. Hence little information is available on the distribution and contribution of major sources of pollution and their impacts to downstream users. This study aimed at assessing the spatial distribution of potentially polluting agricultural and industrial activities, and their contribution to pollution in the catchment. Specifically, the physico-chemical assessment of pollution levels along the river was done, followed by the assessment of river health through biological assessment of macroinvertebrates’ sensitivity and diversity. Furthermore, mapping of the spatial distribution of pollution sources and the estimation of their relation to pollution levels were undertaken. During the study period (February- March 2011), four sampling campaigns at nine points were assessed for physicochemical parameters (including heavy metals), according to Standard Methods. Pollution levels were correlated to the distribution of pollution sources through overlaying landuse and pollution distribution maps and calculating the dominant landuse in a selected buffer area from the sampling points. The GIS work was done using the ArcGIS software. River health was assessed through the diversity of macro-invertebrates according to the SASS 5 Method. Results showed high concentrations of physico-chemical parameters, which give indications of intensive agricultural activities and industrial activities. Total Phosphate showed a maximum concentration of 5mg/l, while TKN reached 120mg/l at the industrial release point. Peak concentrations of Cadmium were observed to be 0.104 mg/l and similar trends existed for other heavy metals. These results were believed to be due to the textile effluent released upstream of the catchment and the increasing rate of agricultural development in the catchment. The results indicated high pollution and implied severe impacts to downstream users. Overall, results for bio-assessment indicated poor biological health of the river due to low diversity, abundance and richness. Statistical analysis confirmed significant differences in the physico-chemical concentrations and bioassessment results along the river at 95% confidence levels. From the mapping, the spatial distribution of pollution and landuse gave indication of the relationships between the pollution sources. The results obtained provided baseline information, which may be used in the development of appropriate Water Quality Management Systems.